A hydrocarbon mixture separated as a decomposition product from naphtha contains various kinds of hydrocarbon compounds.
Among them, 1,3-butadiene, isobutylene, and 1-butene are used as industrially applicable compounds. 1,3-butadiene is used as a raw material of synthetic rubber or plastic.
In addition, isobutylene is widely used to provide a butyl rubber, plastic stabilizers, a gasoline octane number improving agent, tertiary butanol, metacrylic acid, methacrylate ester, and the like. 1-butene may be used for a raw material of a plastic such as a polyolefin or the like.
The method of preparing an alkene compound, particularly isobutylene, includes cracking methyl tertiary butyl ether (MTBA) into isobutylene and methanol, or cracking t-butanol (TBA) into water and isobutylene.
In addition, the alkene compound may be prepared by a liquid homogeneous reaction using p-toluene sulfonic acid. The liquid homogeneous reaction includes: mixing a solvent such as benzene, toluene, xylene, or the like with p-toluene sulfonic acid in a reactor removing water from the mixture according to azeotropic distillation of the solvent and water to obtain a remaining reactant adding a t-butanol aqueous solution including about 15 to 40 wt % of water into a remaining reactant in the reactor; providing water and isobutylene according to the azeotropic distillation; and recycling the remaining solvent layer into the reactor. The obtained water and isobutylene are phase-separated to separate them.
However, since a lot of t-butanol is included in the removed water, there is a concern that the yield may be deteriorated. In addition, p-toluene sulfonic acid is strongly acidic, so a side reaction may occur. The liquid homogeneous reaction also causes problems of excessively using energy during the azeotropic distillation and of difficulty of providing isobutylene having excellent purity.
According to another method, isobutylene may be prepared from t-butanol or a t-butanol aqueous solution including at most 30 wt % of water under the conditions of a reaction temperature of 140 to 200° C., a pressure of 240 to 275 psig, and LHSV (liquid hourly space velocity) of 1 to 5 g/ml and using y-zeolite.
In this case, since the high temperature requires a high energy cost, in order to decrease the reaction temperature, a catalyst of silica-alumina is mixed with a diluent of alumina ceramic or active alumina, so as to further use the mixture as a catalyst. When the silica-alumina is further used, the reaction temperature may be decreased to 140 to 160° C., and the pressure may be decreased to the room pressure.
However, when the silica-alumina catalyst is further used, vapor or nitrogen gas may be further used as a diluting gas, so it may cause problems that the energy cost is increased to provide the diluting gas and to cool the diluting gas.
Furthermore, the method of using the strong acidic ion exchange resin is a method of preparing isobutylene by reacting a t-butanol aqueous solution having a concentration of 40 to 90 wt % with the strong acidic ion exchange resin using the strong acidic ion exchange resin under the conditions of 100 to 130° C., a pressure of 5 to 25 atm,and LHSV of 100 to 300. Thereby, the recycled amount is excessive compared to the raw material amount, so the yield is deteriorated. In addition, it may cause problems of high cost of maintaining the temperature of the recycled material and of transporting the same.